Device for detecting the respiratory activity of a person

ABSTRACT

The invention relates to a method and a device for detecting the respiratory activity of a person and for controlling the time progression of breathing gas pressure, especially in accordance with physical parameters and considering parameters indicating the momentary physiological condition of the breathing person. According to the invention, the device for detecting the respiratory activity of a person has at least one first device that provides a first signal indicating the breathing gas flow v, wherein at least one signal processing device is provided for processing said first signal. The signal processing device is configured in such a way that said device determines a reference relation on the basis of a first signal detected during a first time interval. On the basis thereof, said device determines a correlation relation between the reference relation and the first signal. The device generates an output signal indicating the respiratory activity or the physiological condition of the breathing person by considering at least the correlation relation.

[0001] The present invention is directed to a device for the detectionof the respiratory activity of a person as well as for controlling thetime related course of respiratory gas pressure particularly inaccordance with physical parameters and parameters indicative withrespect to the actual physical condition of a respirating person. Thepresent invention may be applied particularly in the field of sleepmedicine for diagnosing and/or treating sleep related breathingdisorders by positive pressure respiration (CPAP-Therapy). Further, thepresent invention addresses a method for controlling a respiratory gaspressure in connection with excess-pressure respiratory gas supply.

[0002] CPAP-Therapy (Continuously Positive Airways Pressure-Therapy)affords prevention of sleep related breathing disorders in aphysiologically well accepted manner.

[0003] By means of respiratory gas supplied at a defined elevatedpressure level above ambient pressure a pneumatic splinting of the upperairways may be achieved to effectively prevent potential obstructions inthis region—or to afford sufficient Oxygen supply towards the patient incase of temporarily contraction of said upper airways. To achieve highphysiological acceptability it is usually envisaged to adjust a lowrespiratory pressure level affording sufficient pneumatic splinting ofthe upper airways. However, it has become evident that aforesaid lowrespiratory pressure level is subject to significant variations.Experiments have been made by using so called AUTO-CPAP devices whichfor example automatically increase the therapy pressure upon occurrenceof snoring sounds, to take these variations in required CPAP-pressureinto account. Further CPAP-devices are known for detecting the timerelated course of the breathing gas flow and analyzing same with respectto features indicative with respect to airway obstructions. In case ofsuch airway obstructions an increase of the therapy-pressure istemporarily administered.

[0004] Also there are known Auto-CPAP devices determining the presentphysiological condition of a patient by means of pressure pulses appliedto the respiratory gas supplied via a breathing gas conduit wherein forexample on the basis of an impedance detection the present degree ofobstruction may be concluded.

[0005] From EP 0 612 257 B1 there is known a system for generation ofcontinuously positive respiratory gas pressure, which system changes thepressure level of the gas supplied to the patient in a defined manner,and which analyses changes of the airflow profile that may go alongtherewith.

[0006] With respect to the pressure control concepts applied so far forautomatic patient-related adjustment of the breathing gas pressure thereexists a problem in that the changes of the respiratory pressureadministered thereby are not iversally accepted by the respectivepatients. Further there exists a problem in that the known auto-CPAPsystems start to react on significant breathing disorders only.

[0007] It is an object of the present invention to provide a device forthe detection of the respiratory activity as well as for the provisionof physical parameters during administration of a respiratory gas to apatient that allows a precise determination of the physiological stateof the patient.

[0008] According to the present invention this object is performed by adevice for detecting breathing activity of a person comprising at leastone means for supplying a first signal indicative with respect tobreathing gas flow; and at least one signal processing means forprocessing said first signal, wherein said signal processing means beingconstrued so as to generate a reference relation on the basis of saidfirst signal detected over a first time period, and acorrelation-relation between said reference-relation and said firstsignal, said signal processing means being further construed so as togenerate on the basis of an observation of at least saidcorrelation-relation an output signal which is indicative with respectto the breathing activity, in particular classifying same.

[0009] This affords in an advantageous manner an extremely exactclassification of the respiratory activity of the respirating personand, based thereon, meeting the patients physiological state, a precisesetting of the respiratory pressure in a convenient manner withoutdisturbing the natural sleep behaviour. The pressure control based onthe precise classification or detection of the respiratory activityprovides a clearly improved acceptance of therapy and allows a farsighted adjustment of the breathing gas pressure, which may preventoccurrence of potentially occurring airway obstructions with a highlikelihood.

[0010] On the basis of the determination-concept according to thepresent invention it might be possible in an advantageous manner toensure that a patient-specific setting of the breathing gas pressureadjusted by a respective CPAP-device is achieved with high reliabilityand without particular diagnostic efforts. On the basis of thedetermination concept according to the present invention it is furtherenabled to dispense from active variation of the breathing gas pressureas it was so far necessary for the supervision of the physiologicalstate, and to determine the physiological state of the patient withoutarbitrarily adjusted pressure experiments.

[0011] According to a preferred embodiment of the present invention, thelength of a first time period for determining the reference relation isdetermined so as to extend over at least two respiration cycles. It ispossible to define the generation of the reference relation via acriteria-array. This criteria-array preferably includes a plurality ofentries by which it is determined how the reference relation isgenerated from the first and second detected signals. It is possible forexample to determine certain features of the reference relation byprocessing said first and second signals over a period which exceeds ashorter observation period for setting other features of said referencerelation.

[0012] According to a particularly preferred embodiment of the presentinvention there is provided at least one filter-means for filtering thefirst and/or second signal with respect to a predeterminedfrequency-range. This affords to extensive suppression of certaindetection-related noise impacts.

[0013] According to a further preferred embodiment of the presentinvention the signal processing means includes at least one smoothingmeans for smoothing said reference relation by application ofpredetermined smoothing criteria. According to a preferred embodiment,said smoothing criteria are set adaptively. It is also possible toselect preset smoothing criteria for certain respiratory states, or toadapt the smoothing criteria to the detected respiratory state.

[0014] Preferably the parameters of the filter means are adaptivelyadjusted. The adaptation behaviour may preferably determined by input ofrespective parameters.

[0015] According to a particularly preferred embodiment of the presentinvention at least one of the aforementioned smoothing means isconstrued in such a manner that same effects smoothing on the basis ofstatistic methods.

[0016] The generation of output signals which are indicative withrespect to the respiratory activity by means of said signal processingmeans is carried out in accordance with a preferred embodiment of theinvention on the basis of a threshold observation. For this a thresholdobservation means processing threshold criterias in particularzero-crossings is preferably integrated into said signal processingmeans. Preferably, said signal processing means further includes countermeans for counting accomplishment of predetermined criteria within a settime period. Said time periods are preferably variable adapted to thepresent respiratory state.

[0017] The detection of signals indicative with respect to the breathinggas pressure may be carried out for example by means of a pressuresensor which is integrated into a respective CPAP-device and whichdetects for example via a sensing tube the static pressure within aregion of a breathing mask applied to a patient. The signals indicativewith respect to the breathing gas flow may be determined for example viaa sensing shield arrangement provided in a breathing gas supply path.

[0018] By means of the device proposed according to the invention or onthe basis of the analysis procedure carried out by said device a robustdetection of each respiratory cycle of the respirating person isaccomplished. In an advantageous manner the transition from theinspiratory phase into the expiratory phase happens via a characteristicflank on the basis of which a secure detection of each breathing cycleis enabled. In a preferred manner the first derivation in time isestimated. The local extremes of the estimated first derivation of theflow-function correspond to the maximum inclination of the respiratoryflow during transition between inspiration and expiration. Beginning inthe expiration phase the starting point of Inspiration is detected inthat a search through the preceding extreme of the estimated secondderivation is carried out. Further preferred embodiments of theinvention are subject of the dependent claims.

[0019] The length of the first time period is preferably set so as toextend over at least two breathing cycles. Preferably a second means isprovided for provision of a second signal indicative with respect to thedynamic and/or static pressure of the respiratory gas. In a preferredmanner there is provided at least one filter means for filtering ordamping the first and/or second signals.

[0020] The signal processing means preferably includes a smoothingmeans, for smoothing the reference relation by use of selected smoothingcriteria. Said smoothing criteria are preferably adaptively changed. Thesignal processing means preferably includes a smoothing means forsmoothing or damping said reference relation.

[0021] At least one of said smoothing means is preferably construed soas to effect smoothing on the basis of statistical solution-statements.The signal processing means preferably includes a thresholdconsideration means for evaluating said correlation-relation withrespect to threshold criteria in particular zero crossing. The signalprocessing means preferably includes a counting means for countingperformance of predetermined criteria within a preset period of time.The filter-and/or smoothing parameters are preferably adaptively fitted.

[0022] The object of the present invention as mentioned at the beginningis further solved by a device for supplying respiratory gas to a patientat excess-pressure via a feeding means for feeding said respiratory gasand a detection means for detecting at least the breathing gas pressureand/or the breathing gas flow, characterized by a signal processingmeans generating a reference relation on the basis of the detectedsignals and which is setting the breathing gas pressure on the basis ofa correlation between said reference relation and the present breathingpatterns.

[0023] The object mentioned at the beginning is further also solved by amethod for controlling the respiratory gas pressure during CPAP-therapy,by detecting signals indicative with respect to the breathing gaspressure and the breathing gas flow, wherein on the basis of the timerelated dynamic of the measuring values of pressure and respiratory gasflow the presence and/or degree of a flow limitation is detected and thebreathing gas pressure is controlled accordingly.

[0024] 14. Method according to claim 13, characterized in that thetime-points oft the begin of Inspiration- and/or Expiration aredetermined in consideration of the inclination of a curvature portionoft the gas flow by using statistic smoothing methods and wherein asignificant variation of the distance between the ends of Inspiration-or Expiration is determined with respect to a number of subsequentbreathing cycles.

[0025] In a advantageous manner irregularities within the breathing gasflow are detected by comparing the present breath with timely precedingbreathings by application of statistical dependency measurementsPreferably correlation-coefficients and/or mutual-informations aredetected as measurements of dependency.

[0026] Preferably a correlation relation between a reference functionand a present breathing flow is generated, wherein in case of to littlestatistical dependency between the present breath and the timelypreceding breath the respiratory pressure is adjusted accordingly.

[0027] Preferably groups of breathings are standardized via affinetransformation wherein the average curvature of the standardized breathis used for detection of probably existing flow limitations.

[0028] Further the object mentioned at the beginning is also solved by amethod for controlling the breathing gas supply pressure duringCPAP-therapy by detection of the sleeping position of the patient, inparticular the head-position, and/or torsi-position orneck-torsion-degree and wherein the respiratory target pressure and/orthe pressure control characteristic of the breathing gas supply is setin dependency of those detections.

[0029] According to a further aspect of the present invention the objectmentioned at the beginning is solved by a method for controlling thebreathing gas supply during CPAP-therapy including detection of a signalindicative with respect to breathing gas flow, and subjecting thissignal a correlation-analysis on the basis of an adaptively actualizedreference function, wherein on the basis of the results of thecorrelation analysis the physiological state of the patient is typified,wherein with respect to the control of the respiratory gas pressure, inparticular with respect to setting a respiratory target pressure, thecontrol characteristic of a respiratory gas pressure control means isadapted.

[0030] Preferably there are provided several pressure control modesadapted for selected sleep-stages of the patient. The sleeping positionof the patient, in particular the head- and/or torsi-position, and/orthe neck torsion degree are preferably detected in association herewithand the breathing gas target pressure and/or the pressure controlcharacteristic of supplying respiratory gas is set in consideration ofthese detections also.

[0031] Further the object mentioned at the beginning is also performedby a method for controlling the supply of respiratory gas pressureduring CPAP-therapy, including detection of a first signal indicativewith respect to breathing gas flow, wherein this signal subjected to acorrelation analysis based on an adaptively actualized referencefunction, wherein on the basis of the results of said correlationanalysis a physiological state of the patient is typified, wherein independency of the result of typification the breathing gas pressurecontrol is adjusted in such a manner, that same adjusts substantiallyequal static respiratory gas pressure values for inspiration andexpiration within a mask region,—or different mask pressure values forinspiration and expiration (bilevel-mode).

[0032] Further details and features will be apparent from descriptionherein after with reference to the drawing in which:

[0033]FIG. 1 shows (top) a data-portion of a flow graph of a patientduring NREM2; (middle) a high vertical line indicating the end ofinspiration, a low line indicating the begin of inspiration; (bottom)the first derivation in time of the flow-graph on the basis of which theend and the beginning of inspiration may be detected

[0034]FIG. 2 shows (top) a data portion of a flow graph of a patientduring NREM 2; (middle) the last breathing cycle of the data sequenceabove selected as reference relation for the breathing pattern; (bottom)correlation between the data portion above (reference relation) and theflow pattern in the midst;

[0035]FIG. 3 shows (top) a data portion of a flow graph of a patientduring NREM2; (bottom) the average difference of the maxima ofcorrelation from the value 1;

[0036]FIG. 4 shows (top) a data portion of the flow graph of a patientduring REM; (bottom) average difference of the maxima of correlationfrom the value 1;

[0037]FIG. 5 shows (top) a data portion of the flow graph of a patient;(middle) associated CPAP-pressure graph; (bottom) variance of the CPAPsignal per breathing cycle.

[0038] In FIG. 1 the top graph displays 50 seconds of a flow graph of apatient at NREM2-sleep stage. The lower graph of this figure shows anestimated first derivation of the flow graph. Between both graphs thehereby automatically detected transition points are indicated byvertical lines.

[0039] For differentiation between stable and non-stable respirationthere a measurement of similarity of a plurality of successive breathingcycles is considered. The height of a cross-correlation-function is anappropriate measurement for the similarity of the present breathingcycle with preceding breathing cycles. The top graph shown in FIG. 1thereby illustrates the breathing gas flow of a patient during NREM2sleep stage. The high vertical line of the middle graph indicates theend of inspiration, the lower vertical line of the middle graphindicates the end of inspiration. The first derivation of the flow graphwhich allows detection of the end and the beginning of inspiration isillustrated as the lower graph. Because of the different extrema of thefirst derivation of the flow graph it is possible to reliablydistinguish between individual breathing phases.

[0040] The FIG. 2 graph illustrates as an example a 50-second portion ofrespiratory flow of a patient during NREM 2. The middle graph is aselected breathing cycle. The lower graph illustrates the correlationbetween the data sequence (top graph) and said selected breathing cycle.The correlation graph assumes values between 1 and —1, wherein thecorrelation assumes the value 1 in case that both breathing cyclescorrespond to each other exactly,—and the correlation assumes the value—1 when the graphs are correlated negative i.e. a top section ofbreathing pattern exactly meets a valley section of the analyzed dataportion.

[0041] On the basis of the correlation graph it is at first evidentwhether respiration is regular and at second whether breaths are missedcompletely. In case where successive breathing cycles are similar thegraph of correlation will have a periodic course with local maxima closeto 1 and local minima close to −1.

[0042] With respect to the correlation graph illustrated in FIG. 2 thedifference to the value 1 is calculated at each local maxima, whereinall of the thus obtained values are averaged. This average value between0 and 1 may be used as a measurement in how far the breathing patterncorresponds to the preceding breathing cycles.

[0043] In FIG. 3 the top graph illustrates the flow graph of a patientduring NREM 2 sleep stage. The lower data sequence illustrates theaverage difference of the maxima of correlation to the value 1.

[0044]FIG. 4 basically corresponds to FIG. 3 however the flow graph hereresults from REM-sleep stage. The comparison of the average maxima ofcorrelation according to FIGS. 3 and 4 shows that the average differenceof the maxima of correlation to 1 in REM sleep stage is clearly greater.

[0045] The following table illustrates which groups of respiratorystates could be differenciated on the basis of the measurement ofsimilarity as set forth above. stable respiration non stable respirationsilent regular respiration irregular respiration during REM respirationwith associated snoring obstructive apnea mouth breathing awakerespiration periodic breathing with flow limitation Cheyne Stokerespiration dampened respiratory flow signal

[0046] Detection of Snoring

[0047] The detection of snoring may be effected according to a preferredembodiment of the invention on the basis of the variance of theCPAP-pressure within a breathing cycle. In FIG. 5 the top graphillustrates a portion of a respiratory flow signal, there under there isillustrated the corresponding CPAP-pressure. The graph bottomillustrates the variance of the CPAP-pressure per breath. Said varianceclearly increases when the CPAP-Signal is varied due to patientssnoring.

[0048] Further Parameters of Discernment

[0049] The reliable detection of the transition points for beginning andend of inspiration on the basis of the concept according to the presentinvention allows to retrieve further significant features fordistinguishing of breathing states. Particular advantageouslyretrievable indications are the time of inspiration, the time ofexpiration, the maximum flow during inspiration, the maximum flow duringexpiration, the volume of inspiration and the volume of expiration.

[0050] Mouth Breathing

[0051] artefacts due to mouth-breathing may be reliably detected sincein that case a negative correlation is existing. Obstructive apneasmight be detected also in that certain peaks of correlation occur in aclearly weakened manner—or are completely missing in the regular case.

[0052] Flow Limited Breathing

[0053] On the basis of the concept underlying the present invention aflow limited breathing may be made out via the volume of inspiration orthe relative change of the maximum inspiratory flow, in as far asinspiration is flow limited. If the approximate moments for beginningand end of inspiration are known it is possible to determine the momentof maximum inspiration. If this moment is placed in the first half ofinspiration the presence of a flow limited inspiration may be assumedwith high statistical likelihood and a respective correction of therespiratory pressure may be administered.

[0054] Cheyne Stoke Respiration

[0055] A periodic course of respiration showing periodic course of theinspiratory volume is characterizing Cheyne Stoke respiration which isthus distinguishable from other non stable breathing patterns.

[0056] Surveillance of the Detected Breaths

[0057] In a quite advantageously manner the correlation curve may beused for surveillance of the detected moments of beginning and end ofinspiration, since a local maxima in the correlation graph isrepresenting with high statistical saftey a feature of a breath.

[0058] On the basis of the concept of analysis underlying the deviceaccording to the present invention it is possible to detect individualbreath with high statistical likelihood and to make far reachingconclusions with respect to the present condition of the patient. Viathe thus obtained detections it will become possible to adjust thetherapy pressure in a predictive manner and with comparatively smallchanging-gradients in line with the physiological needs of the patient.This affords to a high acceptance of therapy.

1. Device for detecting breathing activity of a person comprisingprovisions for supplying a first signal indicative with respect tobreathing gas flow; and at least one signal processing means forprocessing said first signal; said signal processing means beingconstrued so as to generate a reference relation on the basis of saidfirst signal detected over a first time period; and acorrelation-relation between said reference-relation and said firstsignal; said signal processing means being further construed so as togenerate on the basis of an observation of said correlation-relation anoutput signal which is indicative with respect to the breathing activityor the physiological condition of the breathing person and to adjust thebreathing gas pressure control in accordance with said output signal. 2.Device according to claim 1, characterized in that the duration of saidfirst time period is set so as to cover at least two breathing cycles.3. Device according to claim 2, characterized in that there is provideda second means for supplying a second signal indicative with respect tothe dynamic and/or static breathing gas pressure.
 4. Device according toat least one of claims 1 to 3, characterized in that there is provided aband-pass means for filtering or dampening said first and/or secondsignal.
 5. Device according to at least one of claims 1 through 4,characterized in that said signal processing means comprises a smoothingmeans for smoothing said reference relation on the basis of selectedsmoothening criteria.
 6. Device according to at least one of claims 1through 5, characterized in that said smoothing criteria are adaptivelychanged.
 7. Device according to at least one of claims 1 through 6,characterized in that said signal processing means comprises a smoothingmeans for smoothening said reference relation.
 8. Device according to atleast one of claims 1 through 7, characterized in that at least one ofsaid smoothing means is construed so as to operate on the basis ofstatistic concepts.
 9. Device according to at least one of claims 1through 8, characterized in that said signal processing means comprisesa threshold-observation-means for analyzing said correlation-relationwith respect to threshold-criteria in particular zero-crossings. 10.Device according to at least one of claims 1 through 9, characterized inthat said signal processing means comprises a counting-means forcounting occurrence of predetermined criteria within a predeterminedtime-period
 11. Device according to at least one of claims 1 through 10,characterized in that said bandpass—or smoothening parameters areadaptively changed.
 12. Device for supplying breathing gas to a patientabove ambient pressure, comprising a feeding means for feeding saidbreathing gas and a detection means for detection of the breathing gaspressure and/or the breathing gas flow characterized by a signalprocessing means which generates a reference relation on the basis ofsaid detected signals and which adjusts the breathing gas pressure onthe basis of a correlation between said reference relation and theprevailing breathing pattern.
 13. Method for controlling the breathinggas pressure during CPAP-Therapy including detecting signals indicativewith respect to a breathing gas pressure and the breathing gas flow, anddetermining on the basis of the time-dynamic of the pressure or thebreathing gas flow the presence of a flow-limitation and/or the degreeof a flow-limitation and adjusting the breathing gas pressure in linetherewith.
 14. Method according to claim 13, characterized in that thetime-points oft the beginning of Inspiration- and/or Expiration aredetermined in consideration of the inclination of a curvature portionoft the gas flow by using statistic smoothing methods and wherein asignificant variation of the distance between the ends of Inspiration-or Expiration is determined with respect to a number of subsequentbreathing cycles.
 15. Method according to claim 13 or 14, characterizedin that irregularities within the flow are detected by comparing thepresent breathing cycle with preceding breathing cycles by usingstatistic dependency-measurements.
 16. Method according to claim 15characterized in that as a dependency-measurement there are detectedcorrelation-coefficients and/or mutual-informations.
 17. Methodaccording to at least one of claims 13 through 16, characterized in thata correlation-relation between a reference-function and the actualbreathing gas flow is generated and wherein upon minor statisticdependency between said actual flow and the preceding breathing cyclesthe breathing gas pressure is adjusted accordingly.
 18. Method accordingto at least one of claims 13 through 17 characterized in that groups ofbreathing cycles are standardized by an affine-transformation and thatthe average curvature-radius of a standardized breath is considered forthe detection of flow limitations.
 19. Method for controllingrespiratory gas supply pressure during CPAP-therapy including detectionof sleeping position of the patient, in particular head position, and/ortorsi position, or neck torsion degree, wherein a target respiratorypressure and/or the control behavior of the respiratory gas supply isset in dependency of these detections.
 20. Method for controllingrespiratory gas supply pressure during CPAP-therapy including detectionof a signal indicative with respect to respiratory flow of a patient,wherein said signal is subjected to an analysis of correlation on thebasis of a adaptively actualized reference function, wherein on thebasis of the results of the correlation analysis the physiological stateof a patient is typified and wherein for control of respiratory gaspressure, in particular for setting a target respiratory gas pressurethe control behavior of a breathing gas control means is adjusted on thebasis of the typified physiological state.
 21. Method according to claim20, characterized in that for selected sleep states of the patient thereare provided respective adapted pressure control modes.
 22. Methodaccording to claim 21, characterized in that the sleep position of thepatient, in particular the head position, and/or the torsi position, andor the neck torsion degree are detected and that the respiratorypressure and/or the pressure control behavior are determined inconsideration of these detections.
 23. Method for controllingrespiratory gas supply pressure during CPAP-therapy including detection,of a signal indicative with respect to respiratory flow of a patient,wherein said signal is subjected to an analysis of correlation on thebasis of a adaptively actualized reference function, wherein on thebasis of the results of the correlation analysis the physiological stateof a patient is typified and wherein in dependency of the result oftypification the pressure control is administered so as to providesubstantially the same static respiratory gas pressure in breathing maskregion, or to provide different static mask pressure levels forinspiration and expiration (bilevel mode).